In structural engineering, understanding the different types of loads acting on a structure is fundamental. Every building or infrastructure project must be designed to safely resist these loads throughout its service life. These loads influence the structure’s integrity, safety, durability, and cost effectiveness.

Major Types of Loads in Structural Design

Dead Loads – Permanent Static Loads

Dead loads are permanent and immovable forces resulting from the selfweight of structural and fixed architectural or mechanical components.

Examples

•  Selfweight of slabs, beams, columns, and walls 
•  Roofing systems and ceiling finishes 
•  Builtin elements (e.g., ductwork, flooring systems)

Live Loads – Occupancy & Usage Loads

Live loads are variable and dynamic loads caused by the presence and movement of occupants, furniture, and equipment. These loads depend on the building’s use.

Typical Values

•  Residential 2 kN/m²
•  Office 3 kN/m²
•  Assembly areas 3 – 5.0 kN/m²

Wind Loads – Lateral Environmental Loads

Wind loads are horizontal forces exerted by wind pressure on a structure. Their magnitude is influenced by the terrain, building height, and shape.

Design Parameters

•  Basic wind speed (V, in mph or m/s) 
•  Exposure category (urban, suburban, open terrain) 
•  Building height and geometry 
•  Internal pressure coefficients

Earthquake Loads (Seismic Loads) – Dynamic Ground Motion

Seismic loads result from ground motion during an earthquake, creating dynamic forces within the structure.

Design Considerations

•  Seismic Design Category (SDC) 
•  Site class (soil type) 
•  Building Importance Factor (I) 
•  Response Modification Factor (R)

 Snow Loads – Vertical Environmental Loads

Snow loads are vertical forces due to the accumulation of snow on roofs, especially in cold regions.

Key Factors

•  Ground snow load (pg) 
•  Roof slope and exposure 
•  Thermal conditions (heated vs. unheated structures) 
•  Risk category of the building

Rain Loads – Roof Water Accumulation

Rain loads occur when rainwater collects on flat or lowslope roofs due to inadequate drainage or blockages.

Design Factors

•  Roof slope and drainage design 
•  Clogged drainage scenarios (e.g., blocked scuppers) 
•  Storm intensity and duration

Temperature Loads (Thermal Loads)

Thermal loads are induced by expansion or contraction of materials due to temperature variations.

Influencing Factors

• Coefficient of thermal expansion 
• Temperature range (daily or seasonal) 
•  Restraint conditions and material properties

Impact Loads – Sudden Dynamic Loads

Impact loads are caused by rapid or sudden actions, such as moving vehicles, falling objects, or machinery operations.

Example

Crane supported beams must account for an additional impact factor, typically around 25% of the static load.

Construction Loads – Temporary Loads During Building

These are temporary loads encountered during the construction phase, such as workers, materials, and temporary structures (formwork, scaffolding).

Settlement Loads – Differential Foundation Movement

Settlement loads result from uneven foundation settlement, leading to stress concentrations within structural elements. Proper geotechnical investigation and design help minimize these effects.

Conclusion

Understanding and correctly applying various structural load types is essential for designing safe, efficient, and durable structures. Accurate load estimation prevents overdesign, reduces material waste, and ensures longterm performance. Whether it’s a residential building, a bridge, or a skyscraper—load assessment is the backbone of structural engineering.